Heretofore, side chain liquid crystalline polymers having mesogenic groups in the side chains have been studied for a wide range of applications as functional materials for display elements or recording materials in the electronics field or recently as functional materials useful for nonlinear optical materials or light-controlling glass. These side chain liquid crystalline polymers have a structure in which mesogenic groups are bonded to the polymer backbone by means of a spacer.
As the backbone structure, polymers such as polymethacrylate, polyacrylate, polyether, polyorganosiloxane and polyester are known, and many side chain liquid crystalline polymers have been proposed (For example, Liquid Crystal Polymer, CMC, edit. by Naoyuki Koide (1987); R. Zentel, "Liquid Crystalline Polymers", Kem. Ind., Vol. 37, p. 355 (1988); V. P. Shibaev, "Synthesis and Structure of Liquid-crystalline side-chain polymers", Pure & Appl. Chem. Vol. 57, p. 1589 (1985); T. Chung, "The Recent Developments of Thermotropic Liquid Crystalline Polymers", Polym. Eng. Sci., Vol. 26, p. 901 (1986)).
Further, it has been reported that by means of a spacer, the mobility of the backbone structure and that of the mesogenic groups tend to be independent, whereby orientation of liquid crystals will be facilitated, and by means of a long spacer or a more flexible spacer, a more stable liquid crystalline phase can be obtained (Naoyuki Koide, "Synthesis of Polymer Liquid Crystals", Kobunshi, Vol. 36, p. 98 (1987)). Heretofore, most of the chemical bonds known as such spacers are alkylene groups or oxyalkylene groups. It is reported a spacer containing a siloxane component which is known as a flexible chemical bond (EP-0471577-A; Y. Nagase and Y. Takamura, Makromol. Chem., Vol. 193, p. 1225 (1992)).
However, when spacers consisting of alkylene groups alone are used for the above mentioned backbone structures, the temperatures at which polymers show liquid crystalline phase are usually high, and in most cases, they show no liquid crystalline phase but glass phase at temperatures around room temperature. Further, the side chain liquid crystalline polymers containing siloxane components in the spacer possess problems that synthesis of the monomers requires many steps and also high cost owing to employment of expensive silane compounds, though they show liquid crystalline phase at relatively low temperature because of the flexibility of the siloxane bonds.
In view of such a drawback of side chain liquid crystalline polymers having conventional spacers, it is an object of the present invention to provide a side chain liquid crystalline polymer which exhibits stable liquid crystalline phase at a relatively low temperature, i.e., at room temperature or a lower temperature, by utilizing more effectively a monomer containing a siloxane component in the spacer.